In a TAF, the group 'TEMPO 1418 2SM BR' indicates:

The group breaks into three parts. TEMPO signals a temporary fluctuation rather than a lasting change. 1418 is the period, read as whole hours in UTC — from 1400Z to 1800Z — not as a single time and not as a temperature. And 2SM BR gives the conditions: two statute miles visibility in mist, BR being the code for mist, which is fog-like obscuration with visibility of five-eighths of a statute mile or more. Read together, the forecast expects intermittent spells of two-mile visibility somewhere within that four-hour window, each lasting under an hour and totalling under two. For a remote pilot the number that matters is two statute miles against a three-mile requirement, so any spell that occurs makes the flight illegal while it lasts. Because the timing within the window cannot be predicted, the practical planning response is to treat the whole 1400Z to 1800Z period as at risk.

TEMPO marks a temporary fluctuation, 1418 gives the period from 1400Z to 1800Z in whole hours, and 2SM BR is two statute miles visibility in mist.

TEMPO groups in a TAF give a period in whole UTC hours followed by the forecast conditions. BR denotes mist, with visibility of five-eighths of a statute mile or more; FG denotes fog below that.

Marker, Window, Weather. TEMPO says temporary, 1418 says when, 2SM BR says what.

BR is mist at five-eighths of a mile or more; FG is fog below that. The codes are commonly confused.

• •Reading the four digits as a single time or as temperature
• •Treating TEMPO conditions as continuous
• •Confusing BR with FG